I'd say you are in a state of shock at the moment as the reality of your husband being a serial cheater has finally sunk in.
It's going to be difficult distancing yourself from the emotions you are feeling and the cold hard facts of the situation.
I agree with Pendulum, you ought to confide in your children or perhaps if you have a sister? I gather your children are all grown up and living their own lives? I don't feel you ought to go through this alone and carrying the mental thoughts which you are carrying alone. You do need to speak to someone.
To get you over the worst emotional fears you can visit your doctor and for a few months go on a light dose anti depressant or something to help calm you so that you can think straight.
Something does need to come of this. You can't go on living this way and waiting for his next affair, wondering where he is, who he's with, who he's giving money to. It's not good for your over all health to be sitting at home wondering when his next affair will surface.
It's normal for most of us to look back at the times our partner was 'good' to us. We visualise and feel all those happy and nice moments and they override the bad things which are going on now. In reality, you ought to be focusing on the bad, this makes us angry and makes us take action.
I went through the same thing when i had to leave my husband. I saw no future staying, i'd taken every avenue possible in helping our marriage, but he wouldn't meet me half way so i had to leave. It was the best thing i did. At the time i was scared as hell. I felt as though i was standing on the edge of a cliff and had to jump. Once you take the first step and leave it's like this amazing calm washed over me.
At the end of the day it's your choice and you know what you can and can't do, but you do need to face reality and realise that he wont change. I don't think he's just into the affairs with other women, he could be into forms of sex which the two of you haven't been inclined to perform together. Who knows what fetishes he has. This is no excuse and the fact he's lying to you and not being honest about why he needs to do this with other women when you are more than willing is enough to ring alarm bells.
Can you get some counselling? and if things get so bad that you can't cope, you will need to speak to someone or get some temporary medication. There are good things out there which are non addictive. I was on some antidepressants for about 4 months due to not being able to sleep or eat at all. It calmed me, enabled me to get sleep and brought back an appetite. When you are calmer you can think more straight too. Best wishes